The present invention relates to a voice conference apparatus capable of establishing a voice conference between remote places by employing the communication means (the communication network).
Very recently, voice conference apparatuses capable of establishing voice conferences between remote places by employing communication means have been gradually popularized. It is desirable that such voice conference apparatuses have been designed in such a way that even when a plurality of persons are present at respective installation places of these voice conference apparatuses, these plural persons can operate the voice conference apparatuses. As a typical apparatus example, the below-mentioned telephone conference apparatuses have been proposed (refer to, for example, patent publication 1). That is, one typical telephone conference apparatus includes a plurality of microphone devices for converting audible sounds into electric signals; a loudspeaker for converting the electric signals into audible sounds; and a voice communication network for electrically connecting these microphone devices and the loudspeaker to a telephone line. Each of the microphone devices has such a directional polar sensitivity characteristic which has a high sensitivity with respect to sounds which are radiated from at least one direction, as compared with sounds radiated from other directions. Furthermore, the directional polar sensitivity characteristic has a main lobe, side lobes, and a null present between paired lobes. The loudspeaker is arranged at a position of the null of the directional polar sensitivity characteristic, which is located between the side lobes adjacent to the main lobe.
The loudspeaker provided in this telephone conference apparatus has been installed at the null of the polar sensitive patterns as to the main lobe and the side lobes adjacent to the main lobe. As a result, acoustic coupling effects between the loudspeaker and the microphone devices are essentially reduced, so that the telephone conference apparatus can be operated in a full duplex mode, that is to say, while voices of the counter panties are mutually outputted from the loudspeakers so as to hear stories, persons can produce voices by employing the microphone devices.
While each of the microphone devices utilized in this telephone conference apparatus has one or plural pieces of microphones, directional microphones are used as the respective microphone devices in order to establish desirable sensitivity characteristics.
[Patent Citation 1] U.S. Pat. No. 5,121,426 (JP-A-3-293846)
However, the directional polar sensitivity characteristics of the directional microphones have characteristic fluctuations in view of manufacturing aspects, and magnitudes of the main lobes and the side lobes, and also, the null positions are difference from each other as to the respective directional microphones. Also, in such a case that the directional microphones are installed within an apparatus, these directional microphones may be readily influenced by peripheral structural components thereof. Moreover, as to the directional polar sensitivity characteristics of such microphones, the magnitudes of the main lobes and the side lobes, and also, the null positions are changed due to aging effects thereof. As previously described, there is such a problem that the sensitivities of the directional microphones are unstable, and thus, qualities as to the full duplex communication of the telephone conference apparatus are lowered.